The performance of microwave high power amplifiers (HPAs) is a key driver to establish overall satellite communication (SATCOM) payload performance. The total direct current (DC) power consumption within a communications satellite (COMSAT) is primarily based on the HPA DC to radio frequency (RF) efficiency at a given RF output power level; the DC to RF power-added efficiency (PAE) of the HPA is a key measure of performance. Fixed satellite service (FSS) and mobile satellite service (MSS) communications each require operation of the HPAs under multi-carrier operation to meet demanding high volume traffic conditions. Typically, for SATCOM frequencies at UHF (225-400 MHz), L-band (1.2-1.8 GHz), S-Band (2-3 GHz) and C-Band (3.7-4.2 GHz), solid-state-power amplifiers (SSPAs) are the preferred method of HPA implementation vs. heavier and more expensive travelling wave tube amplifiers (TWTAs), and can be used individually or in combination within a multi-port amplifier (MPA) configuration for maximum flexibility.
For these communications systems, the minimization of distortion under multi-carrier operation to avoid interference between SATCOM users is critical to maintain high quality of service. High linearity within the HPA to reduce spectral regrowth due to generation of inter-modulation distortion (IMD) needs to be maintained for varying operating conditions. In a multi-carrier operation, a very good indicator of linearity is a good NPR (noise power ratio).
Additionally, based on traffic conditions, the HPA output power will vary over a significant RF power range, typically 5 dB or greater; maintaining IMD, NPR and PAE performance over this range of RF power output levels are typically in conflict, resulting in either a sacrifice in NPR or PAE performance resulting using conventional techniques.